We demonstrate that current pharmacopoeial methods are inadequate for the detection of this type of adulteration, and we propose a simple modification of the USP-NF method that addresses this problem.
The flavonol glycoside content of the retail products, calculated both pre and post hydrolysis using the formula provided for Content of Flavonol Glycosides in the USP-NF monographs, is shown in Table 3.
All products conformed to the relevant USP-NF monographs with respect to flavonol ratios after acid hydrolysis.
The pharmacopoeial methods for determining the content of flavonol glycosides in ginkgo extract and products differ somewhat between the USP-NF and BP/EP monographs, but in both cases the glycoside content is calculated from the content of free flavonol aglycones, quantified by HPLC following acid hydrolysis.
As an aid to detecting adulteration of ginkgo extracts, the USP-NF monographs for Powdered Ginkgo Extract (but not the equivalent EP/BP monograph), Ginkgo Tablets and Ginkgo Capsules include specifications for the relative abundance of quercetin, kaempferol and isorhamnetin after acid hydrolysis.
Thus, we have identified three adulterated ginkgo retail products, all of which conformed to the relevant USP-NF monographs (Ginkgo Tablets or Ginkgo Capsules) in terms of ratios of HLPC peak areas between kaempferol and quercetin and between isorhamnetin and quercetin in hydrolysed samples (Fig.